Increasingly, the potential dangers inherent in operation of commercial and other aircraft in the presence or vicinity of dangerous windshear conditions are being recognized. With such recognition and the development of data representative of the presence of airborne windshear conditions, the capabilities of airborne radar systems have been adapted for detection of conditions indicative of windshear. Two attributes of such detection are significant. First, the indicative conditions are difficult to detect and evaluate when present, thereby requiring regular testing of radar systems to ensure that operation is adequate to meet relevant windshear detection standards. Also, actual windshear conditions are relatively rare and unpredictable, so that the simulation of indicative conditions must be reliably employed in radar system testing. These and other relevant factors establish the need for reliable test systems and methods for field testing aircraft-installed windshear radar systems accurately, reliably, without radar system disassembly, without extended out of service periods, and without requiring complex test equipment or test set ups.
The flight hazard represented by the presence of windshear conditions may be represented by a so-called "F-factor". The F-factor has been used as a non-dimensional hazard index directly related to the rate of climb capability, or lack thereof, of an aircraft in windshear. Negative values of F indicate a performance-increasing situation and positive values indicate increasingly threatening conditions. Under windshear conditions in a microburst downdraft region with wind vertically downward, a positive F-factor will indicate a potentially dangerous situation.
An airborne windshear detection radar typically derives horizontal wind velocity values by Doppler measurement of radar returns from aerosols, raindrops and other materials which may be dispersed in the air (all of which tend to move with the same velocity and direction as the horizontal air movement or wind). Differences in horizontal wind velocity as a function of range thus permit estimation of the rate of change of the horizontal component of windshear. However, known types of airborne radar systems cannot measure wind velocities perpendicular to the radar line of sight. This inability to measure vertical (downdraft) velocity represents a serious factor in the ability to evaluate windshear phenomenon under actual flight conditions. In view of this, significant effort by workers in this field has been directed to developing methods for estimating vertical wind velocity under various conditions from radar horizontal wind measurements, in order to improve F-factor calculation accuracy. Existing and possible future improved methodologies for evaluating and simulating windshear effects and conditions may advantageously be taken into account for radar testing purposes.
It is therefore an object of this invention to provide portable and economical test systems which are readily field deployable to test windshear detection capabilities of aircraft radar systems.
An additional object is to provide such test systems able to monitor radiated windshear radar signals from distances of the order of fifty feet and radiate back to the radar test signals which have been responsively proportioned and may include windshear simulation test data.
Further objects are to provide new and improved test systems and methods, including such systems and methods suitable for field testing of radar systems by use of radiated test signals which are amplitude modulated and timed for near real-time response to reception and analysis of signals currently radiated by a radar system under test.